1. Field of the Invention
The present invention relates to telephones. It relates particularly, but not exclusively, to test telephones.
2. Description of the Prior Art
A telephone that is to be manufactured for export to a number of countries must be adaptable to comply with the signalling and functional protocols used by the telephone exchanges of the various countries. Typically, a different protocol is required for each country. Techniques have been developed for adapting telephones to different systems. However, these techniques have involved long lead-times, high costs for each new protocol, and only limited scope for change once a protocol has been implemented.
Many telephones now are supplied with memory functions such as last number redial and storage of commonly used numbers. In known telephones, these functions have been implemented using volatile memory maintained by primary batteries, a small current drawn from the line, or secondary batteries and a small line current. Batteries are expensive and liable to cause data loss on discharge, and small line currents are undesirable and disallowed in some countries.
When a telephone is used in a high noise environment, hearing the received signal can be a problem: (a) because the ambient noise is heard in the receiver as side tone and (b) the noise break-through through the telephone handset and the user's skull and sinuses dominates the received signal.
If the gain of the receiver were increased with the microphone unmuted it would produce two problems: (a) amplifed side tone with no improvement in the signal to noise ratio; (b) the telephone would have a tendency to generate acoustic feedback.
Embodiments of the invention may enable one to ameliorate one or more of the above problems.